Circuits of this type are well known since they have many advantages, particularly in small timepieces. In this case the supply voltage is provided by a battery. Depending on the type of battery, its nominal voltage may vary considerably. Thus, a mercury battery has a voltage of 1.35 V, whereas silver and lithium batteries provide 1.5 V and 3 V respectively. With a conventional control circuit which supplies drive pulses of an amplitude equal to that of the power supply it is, of course, impossible to replace one type of battery by another without upsetting the operation of the motor. This is a major disadvantage, because each type of battery has to correspond to a specific circuit, and because this causes after-sale service problems.
By contrast, this does not raise any difficulties with a control circuit supplying drive pulses the mean voltage of which is independent of variations in the input voltage of the power supply, it being possible for these variations to result either from the replacement of the battery by another one of a different type or from the state of discharge of a given battery. The mean voltage of the drive pulse may, moreover, in the case of a circuit of this type, be set at a value considerably lower than that of the voltage of the battery. This is a substantial advantage since the coil of the motors intended to be driven by such a circuit may then be made of a wire of large cross section, i.e. a wire that is cheap and easy to work, making it possible to reduce the price of the motor.